Dynamo-electric machinery.



PATENTED MAY 26, 1903;

H. M. HOBART.

DYNAMO ELECTRIC MACHINERY. 7

APPLICATION FILED FEB. e, 1902.

v1T0 MODEL.

invention- Hsnry mrlobart. y

- Amy Witnesses.

UNITED STATES Patented May 26, 1903.

PATENT OFFICE.

DYNAMO-ELECTRIC MACHINERY.

SPECIFICATION forming part of Letters Patent No. 729,17 5, dated May 26,1903.

Application filed February 6, 1902. Serial No. 92,794. (No model.)

To (tZZ whom it may concern:

Be it known that I, HENRY M. HOBART, a citizen of the United States,residing at Berlin, Germany, have invented certain new and useful Improvenlentsin D ynamo-ElectricMachinery, of which the following is aspecification.

My present invention relates to means for reducing sparking at thecommutator in dynamo-electric machines of the commutating type. Tosecure this result, I provide means for reducing the self-induction ofcoils undergoing commutation.

The novel features which I believe characterize my invention I havepointed out with particularity in the appended claims. The inventionitself, however, its construction and mode of operation, will be betterunderstood by reference to the following description, taken inconnection with the accompanying drawings, in which Figure 1 representsone embodiment of my invention, and Figs. 2 and 3 modified formsthereof.

The various embodiments of my invention which I have shown in thedrawings will be found to be characterized by the existence ofshort-circuited conductors placed in good inductive relation to the endconnections of the armature-windings. These conductors perform thefunction of short-circuited secondaries and by their reaction uponvariable currents in the said end connection act to reduce theself-induction of the armature coil or coils of which the endconnections are a part. This reduction in the self-induction of coilsundergoing commutation reduces the sparking which takes place as thecommutator-segments connected to the winding pass out of contact withthe commutator-brushes. The decrease in self-induction which may be madeby the use of my invention may be considerable, since in modernmachines, and particularly in those having short armatures of largediameter, a very large proportion of the total inductance of the coilundergoing commutation resides in the end connections, for althoughthese parts are not embedded in slots they constitute a very highpercentage of the total length of the coil.

In Fig. 1 a longitudinal section of a portion of an armature is shown.This armature is of ordinary construction so far as concerns the spider1, the ventilated laminated core 2, and the shaft 3 by which they arecarried. At lis represented a conventional view of one of the endconnections of the armature-winding. It will of course be understoodthat the upper and lower portions of this end connection do not passthrough the same slot in the armature, although for convenience ofillustrationit might besupposed from the drawings that such is the fact.The main feature which this figure is intended to illustrate is,however, not the connections of the armaturecoils, but the fact that theend connections are of loop form, such as to produce an annular spacewithin the end connections. This space is filled, except for room takenup by insulation, bya ring-shaped mass 5 of good conducting material,such as copper or brass. X This mass, if desired, might be made hollow,the latter construction being intend ed for use Where the Weight or costof the additional material is for any reason prohibitive. Whicheverconstruction is employed, the ring acts as a short circuited secondaryfor the end connections looped about the same and acts to reduce theselfinduction of these end connections while they are undergoingcommutation and also under any other conditions which cause fluctuationsof current therein. The short-circuited ring 5 may be built into theannular space in the end connections in any suitable manner duringconstruction of the machine. In the particular arrangement shown theupper and lower parts of the loops 4 are disconnected while the armatureis in course of construction, the ring being put in place after thelower portions 7 of the end connections are assembled and the ends ofthe loop then joined by suitable connecting means, such as indicated at8. In order to increase still further the amount of secondary conductorsinductively related to the end connections, I

may make the supporting-drum 9 for the end connections of goodconducting material, such as copper. The drum itself then becomes theseat of more or less strong induced currents, and thereby reacts toreduce the self-induction of the end connections, which operate as theprimary inducing-windings.

In Fig. 2 a somewhat difierent arrangexnent is shown. In this instancethe end connections 10 are not looped, as in Fig. 1, but extend out fromthe armature-core l1 and are supported by the cylindrical end druml2,carried by the armature. This drum is formed of copper, brass,:orother good conducting material and is provided with a flange 13, whichextends outwardlyand to which is secured one edge of a ring let, whichsurrounds the outer surface of the end connections. The inner edge 15 ofthis ring is electrically connected at numerous points with theconducting-drum 12. One of these connections is indicated in dottedlines at 16; but it is to be understood that these connections are madeas numerous and of as large an aggregate current-carrying capacity as isconvenient in order that they may complete a good conducting-path forinduced currents across the drum 12, the flange 1:3, and the ring 14.Space for these connecting-conductors may be found opposite each toothof the armature-core. 1 i a Fig. 3 shows an. arrangement in which theshort-circuited conductors acting as secondaries to the end connectionsare formed'not of masses of'conducting metal, but of shortcircuitedwindings interspersed with the'end connections. In this figu'ge, whichrepresents a developed view of a portion of an armature and its winding,the teeth of the armaturecore are represented by the numeral 17, appliedto one of these teeth; The slots between the teeth carry the armatureconductors represented, for example, by the two lines 18, one a lightfull line corresponding to the outer coils of the armature-slots and thedotted line to the inner coils. The end connections for the respectivecoils are represented by lines of the same character-as, for eXample, at19. Interspersed with these end connections are conductors,(representedin heavy lines at 20,) the arrangementof these conductors being the sameas the arrangement of the end connections of the armature-coils. Theseconductors,which are interspersed with the'end connections, instead ofpassing into the slots of the armature, as in the case of thearmature-windin g proper, are all connected together by a conductingmember or bar 21, located adjacent to the ends of the armature-teeth.The conductors 20 and the connecting-conductor 21 therefore furnishnumerous paths closed upon themselves, wherein currents may be inducedby the influence of current fluctuations in the end connections. Theseclosed conducting-paths being in very close mutual inductive relationwith the end connections form a very effective means for reducing theself-induction of the armature-coils, of which the end connections are apart. 7

What I claim by Letters Patent of the United States, is

1. The combination with an armature-wind ing, ofpermanently-short-circuited conductors in close mutual inductiverelation to the end connections ofsaid winding and adapted to form theseat of induced currents.

2. In a dynamo-electric machine, the combination of a windingprovided'with end connections, and permanently-closed circuitedconducting-paths in inductive relation to said end connections andadapted to form the seat of induced currents.

3. The combination of an armature-winding provided with end connections,and closed conducting-paths located away from the active portion of thearmature-winding but in inductive relation to the end connectionsthereof, said conducting paths adapted to form the seat of inducedcurrents.

4. The combination of an armature-winding provided with end connections,and permanently-closed conducting-paths of copper in good mutualinductive relation to said end connections. I

5. The combination of an armature-winding provided with end connectionsportions of which lie on the outside of the armature and other portionsthereunder, and good conducting material located adjacent both to the inner and outer portions of said end connections. r

6. The combination of an armature-winding provided with end connectionsof which one port-ion lies within another portion, and closed circuitedconducting-paths located adjacent to both the inner and outer portionsof said end connections.

7. In a dynamo-electric machine, the combination of a winding providedwith end connections, and means in close mutual inductive relation tothe end connections of the winding for reducing the self inductionthereof.

In witness whereof I have hereunto set my hand this 17th day of January,1902.

. HENRY M. HOBART.

Witnesses:

HENRY HASPER, WOLDEMAR I-IAUPT.

as new, and desire to secure

